Short Adapter Shank #77 is the shortened version of Standard Adapter Shank #75.
Serving as a connecting piece between needle bar and accessory, Short Adapter Shank #77 allows other manufacturers’ presser feet to be used on BERNINA machines.

If these feet are short-shanked, they won’t fit on the machine’s standard holder without an adapter.
By contrast, Standard Adapter Shank #75 is used e.g. with BERNINA sewing accessories such as Simple binder #85 or Ruffler attachment #86.